Remark 3.1.3 
From the definition, (see also [1]}), there is a
short exact sequence
\(  0\rightarrow {E}\hspace{-1.0pt}nd(E, P^\bullet )\overset{\iota }{\rightarrow } \operatorname{At}_C(E,P^\bullet )\overset{\delta }{\rightarrow } T_C\rightarrow 0,\) 
